Synthesis of 2-pyridones and derivatives thereof

ABSTRACT

2-Pyridones are conveniently synthesized from 2,4-pentadienoic acids by formation of the acid azide, decomposition of the azide into an isocyanate and the simultaneous cyclization of the isocyanate into the pyridone. The pyridones are readily converted into known pyridines.

Berijckere et al.

[151 3,666,765 [4 1 May 30, 1972 SYNTHESIS OF Z-PYRIDONES AND DERIVATIVES THEREOF Antoon M. Beriickere, Uccie; Fernand G. F. Eloy, Genese, both of Belgium Union Carbide Corporation, New York, N.Y.

Filed: Oct 27, 1969 Appl. No.: 869,862

Inventors:

Assignee:

U.S. Cl ..260/290 HL, 260/290 P, 260/297 2, 260/294.8 D, 260/297 R, 260/294.8 F, 260/294.8 E, 260/294.9, 260/247.2 A, 260/293.69, 260/349, 260/347.3, 260/332.2 A, 260/453 P, 260/296 R, 2.60/346.l R, 260/329 R, 260/86. 1, 260/240 J, 260/240 D Int. Cl. ..C07d 43/06 Field of Search ..260/297 Z, 290 P, 290 HL, 294.8 F, 260/294.8 D, 294.9, 296 R, 297 R, 247.2 A, 294

AC, 247.5 R, 293 D, 240

[56] References Cited UNITED STATES PATENTS 3,393,!99 7/1968 Daum et al ..260/297 2 7 Primary Examiner-Henry R. Jiles Assistant Examiner-S. D. Winters Attorney-Paul A. Rose, Gerald O'Brien and -William R. Moran [57] ABSTRACT 2-Pyridones are conveniently synthesized from 2,4-pentadienoic acids by formation of the acid azide, decomposition of the azide into an isocyanate and the simultaneous cyclization of the isocyanate into the pyridone. The pyridones are readily convened into known pyridines.

17 Claims, No Drawings SYNTHESIS OF 2PYR1DONES AND DERIVATIVES THEREOF This invention relates in general to the synthesis of 2- pyridon'es and derivatives thereof. In one aspect this invention is directed to a novel process for the preparation of 2- pyn'dones and derivatives thereof. In a further aspect, this invention is directed to a novel process for the preparation of pyridines.

Heretofore pyridones and pyridines have been prepared by a variety of methods reported in the literature. For example, pyridine compounds have been prepared by the Chichibabin Synthesis which involves the reaction of aldehydes and ketones with ammonia. Additionally, pyridine compounds can be prepared by the l-lantzsch Synthesis, e.g., the condensation of acetoacetic ester with an aldehyde in the presence of ammonia.

The pyridones have been prepared by the decarboxylation of the hydroxypyridinecarboxylic acids. Moreover, it has been reported that N-alkyI-Z-pyridones are formed from 2-chlorol-alkylpyridinium halides with aqueous sodium hydroxide.

It has now been discovered that 2-pyridones and their pyridine derivatives can be conveniently prepared in high yields from readily available starting materials. The process is simple, efficient and provides a novel route to 2-pyridones which can easily be converted to the corresponding pyridines.

it is therefore an object of this invention to provide a novel synthesis for the preparation of Z-pyridones. Another object of this invention is to provide a novel process for the synthesis of 2-halo-pyridines. A-further object of this invention is to provide a process for 3-substituted pyridines. A still further object of this invention is to provide a process for the preparation of 2-pyridones which can be obtained in relatively high yields. Another object is to provide a process which is simple and efficient. These and other objects will readily become apparent to those skilled in the art in light of the teachings herein set forth.

In its broad aspect, the present invention comprises a method for the synthesis of Z-pyridones of the formula:

sulfonyl, benzylthiomethyl, alkythioalkyl, dialkylamino, morpholino, arylthiomethyl, styryl, cycloalkyl, benzoyl, trihydrocarbylsilyl, benzyloxy, furyl, thenyl, dialkoxyalkyl,

piperidinomethyl, aryloxyalkyl, benzoylvinyl, and admantyl.

The process comprises heating a 2,4-pentadienoic acid azide of the formula:

wherein R,-R are as above, at an elevated temperature for a period'of time sufficient to produce the Z-pyridone.

The overall reaction involves the Curtius degradation of a 2,4-pentadienoic acid azide to a butadienyl isocyanate and cyclization into the pyridone in accordance with the following reaction:

wherein R R., are as defined above.

Preferred Z-pyridones which can be prepared by the process of this invention are those wherein the group consisting of hydrogen, alkyl, aryl, alkaryl, aralkyl, alkoxy, alkoxyalkyl, alkoxyaryl, 2-furyl, 3-furyl, Z-thienyl, and 3-thienyl.

The starting materials employed in the process of this invention are the azides derived from 2,4-pentadienoic acids by known synthetic techniques. For example, the unsaturated acid can be reacted with thionyl chloride to form the corresponding acid chloride in accordance with the known reaction described by Fieser and Fieser (2nd edition) on page 183. The acid chloride is then reacted with sodium azide to produce the corresponding acid azide (Ref. F ieser and Fieser, 2nd Edition, pg. 299). Ifdesired the azide can be produced in one step from the acid by using the method of G. Weinstock, J. Org. Chem. 26, 3511 (i961). 1

. Illustrative acid azides which can be employed in the process of this invention include, among others, such compounds as:

2,4pentadienoyl azide,

2,4-hexadienoyl azide,

2,4-heptadienoyl azide,

2,4-octadienoyl azide,

2,4-nonadienoyl azide,

2,4-decadi'enoyl azide,

5-phenyl-2,4-pentadienoyl azide,

5-naphthyl-2,4-pentadienoyl azide,

5-methoxy-2,4-pentadienoyl azide,

S-m-methoxyphenyl-Z,4-pentadienoyl azide,

5-( 2-thienyl)-2,4-pentadienoyl azide,

- 5-(Z-furyl)-2,4-pentadienoylazide,

2-p-methoxyphenyl-5-phenyl-2,4-pentadienoyl azide,

and the like.

As hereinafter indicated, the process of the invention. comprises heating the acid azide at an elevated temperature for a period of time sufficient to produce the condensed pyridone. The exact temperature to which the azide must be heated in order to produce the condensed pyridone is dependent, in part, upon the exact nature of the reactant. In general, however, the reaction occurs at a temperature within the range of from about 200 C. to about 300 C., and preferably from about 200 C. to about 280 C. It is convenient to carry out the reaction by refluxing the azide in an inert, liquid reaction medium that boils within the temperature range indicated above. Such reaction mediums include diphenyl ether, the dibutyl diether of diethylene glycol, the acetate ester of the monobutyl ether of diethylene glycol, benzophenone, dimethyl phthalate, and the like. Diphenyl ether is the preferred reaction medium.

The exact reaction time varies to an extent, depending upon I the exact nature of the azide, reaction medium, and the temperature. In most cases, the reaction will be completed in from about one-half to about four hours, and preferably from about one to about three hours.

As hereinbefore indicated the acid azide is converted by heat to the corresponding isocyanate which then undergoes cyclication to produce the pyridone.

Hence, the isocyanate can be produced in situ by the Curtius Rearrangement of the corresponding acid azide. This can be done by heating the azide at a relatively low temperature, for instance of from about 60 to C., until evolution of nitrogen ceases, after which the reaction mixture is heated to a higher temperature to efiect the ring closure reaction. However, a preferred way is to slowly introduce the acid azide into boiling reaction medium.

It is preferred to include a high boiling tertiary amine in the reaction mixture Such amines include tri-(tert-butyl)amine, tripentylamine, trihexylamine, and the like. The tertiary amine can be used in varying amount, such'as from about 5 mole percent to about 300 mole percent, and preferably from about 50 mole percent to about mole percent, based on the moles of azide used.

R -R contain up to 12 carbon atoms and individually represent a member selected from I The isocyanates formed from the azides and used in the process of the invention contain unsaturation which is capable of undergoing polymerization under certain conditions, as will be readily understood by chemists. Accordingly, it is desirable and acetic acid to substitute a hydrogen atom for the halo group to form a pyridine, and the like. All of these reactions are known type reactions.

The halogen pyridines can also be converted to the corto carry out the process of the invention in the absence of free 5 responding pyridine by reduction in accordance with the folradical polymerization promoters, which includes oxygen. In lowing equation: many cases, the boiling reaction medium will provide a sufiiciently inert atmosphere to avoid excessive loss of yield due to polymerization of the reactant and/or product. However, it may be desirable in some cases (such as when isocyanate con- R tains a reactive substituent group such as a vinyl group) to add 2 R4 R2 a free radical polymerization inhibitor to the reaction medi- R1 N *9 R1 N um. Such inhibitors can be used in customary amounts, which are well known in the art. I

The condensed pyridone product can be'recovered by conventional procedures. For instance, the reaction medium can be removed by distillation under vacuum, the pyridone can be wherem X and R1-R4 are same as mdlcated above- Reducdissolved in diethyl ether, and then recrystallized from a concan be effected by one or mokje f known venient solvent. The examples below illustrate the solvents methods Such as for mR by reducmg Wlth Zmc metal in that can be used for the recrystallization. When a high-boiling the pre sence of acenc acldother methods can also be tertiary amine is used in the reaction, it is most conveniently emphaslzefi removed by vacuum distillation along with the reaction medi- As ffi mdfcatedr the 'P Prepared y the umprocess of this invention are particularly useful as reaction in- The pyridones of the invention are widely useful as reaction termedates the prfeParauon of known Pyridines and intermediates. For instance, they can be reacted with the acid hal0gen'sfbmuted Pyndmeschlorides of drying oil acids to form N-acyl derivatives which The lfi f themelves r a class of gomposmons having can be used in air-drying surface coating formulations in acunmy m a wlde vanety of fields- For example, the cordance with' known techniques. The furoand thienopynd'mes are useful as accefptors for Y hzflides which pyridones which have the 2,3-double bond unsubstituted can are formed as byproducts con'fiensancfn reactions and as be copolymerized with vinyl type monomers to form useful solvents for ,umerous orgamcandmofgamc P copolymers. For instance, such furoand thieno-pyridones The followmg examples aremustrauve' can be first reacted with the acid chloride of a long chain al- EXAMPLE 1 kanorc acid such as stearrc acld to'form the N-acyl derivative, which can then be copolymerized with acrylate monomers Preparation of 3-Methyl-2-Pyridone such as methyl methacrylate to form copolymers that have utility as viscosity index improvers for lubricating oils. one P of mfsthylamme m 400 cc of acetone was The invention also provides pyridine derivatives of the conoduced m a 50mm, of g mole) of sorpic acid ill densed pyridones described above. Such derivatives include 3 00 cc of Same solver, the F bemgmalmained at those that are prepared by reacting a phosphorus halide with 40 0 C. A solution of 1.1 mole of ethyl chloroformrnate in 400 cc the pyridone toproduce the halGPYridine in accordance with of acetone was then slowly introduced in the cooled mixture. the reactions. After 30 mm. stirring, 1.3 mole of NaN in 300 cc of water was added dropwise at 0 C. The mixture was stirred for an addi- Ilh tional hour and poured on 4,000 ml H O. The azide 2,4-hex adienoyl azide, was then extracted with methylene chloride or R2- R4 POxa R benzene and the solution was dried on NaSO or P 0 This NH N solution was used for the following reaction: Ri- R1 in a distillation vessel containing a boiling mixture of 1 liter 8 2 C of diphenyl ether and 185 g of tributylamine, the solution of crude azide was slowly introduced at such a rate that the low wherein RF 4 are as above and X represents habgem boiling solvent was continuously eliminated. The temperature chloro or bromo. The reaction of a pyridone with phosphorus of the T was Pamtained at 220L240 during the noxychloride or phosphorus oxybmmide to produce a halo troductron of the azrde and one hour after. The mixture was pyridine is a known type of reaction which is further then concentrated in vacuo and ether was added to complete trated by the examples which follow. The invention also prothe preclpnauof of the pyndonecrude P W85 lvides substitution products of the halo-pyridines which are wasPed ether and crystalhzed from p -P- prepared by reacting the halo-pyridine with a primary or a new of percent of 'py was secondary amine to produce an amino derivative, with thioutamed rea to produce a mercapto derivative, with alkali metal alkox- 60 EXAMPLES ide to produce an alkoxy derivative, the reaction of an alkali metal alt of an cyano compound that has at least one In a manner to that set forth in Example 1, other hydmgen attached to the carbon atom l h to h cyano pyridones were prepared from the appropriate starting materigroup to form an alpha-cyano derivative, with methyl iodine The Products Obtained and amYZticaI data are Set fOITh in to form the N-methyl iodo derivative, the reaction with zinc 5 Table IbelOWI TABLE I Analysis l Calculated Found Example Starting acid Product C H N C H N 2 .i b-phcnyl-2,4-pentadienoic acid 3phonyl-2-pyrldonn s s 47 224-226 77. 2O 5. 26 8. l) 76. 50 5. 44 8. 50 3 5-m. mnthoxyphenyI-ZA-punt: ioic. i 3-m. ninth0xyphnnyI-Z-pyridonu, N2 173 71. 5. 47 (i. 96 71. 48 5. 70 h. 68 4 2-p. methoxyphenyl-fi-plmnyl-ZA- 6-p. mnthoxyphcuyl-3-phcr1yl-2- 252 78. 00 5.41 5.06 77. 94 5.48 5.00

ponmrliennic. pyririuun. 5 6-(2-thionyl)-2, i-pcntn limmic r 3(2thlenyl)-2-pyridone s V s (i6 183 61. 00 3. 95 7. H1 60. 88 4. l8 7. 79 (5 5-(2-l'uryl)2,4pi .ntndimmic. .V 55 67.10 4. 35 8. 70 66.92 4.40 8.73

3-(2-luryl)-2-pyridorm EXAMPLE 7 What is claimed is:

l. A f

Preparation of z chloro 3 phenylpyridine from 3 Phenyl 2 mula: process or the preparation of 2 pyndones of the for Pyridone R A mixture of l7.l g (0.1 mole) of 3-phenyl-2-pyridone and 5 I 25 g of POCl was boiled for 4 hours and then evaporated. The R R4 residue was treated with ice and extracted with ether. After evaporation of the etheral solution, the remaining chloro R1 NH derivative was isolated by distillation: B.P. 108 C/O. 1 mm Hg. Yield: 41 percent of 2-chloro-3-phenylpyridine. 0

A l i wherein R -R each contain up to 18 carbon atoms and incalculated: C 69.70 H4.23 N7.39 dividually represent hydrogen, hydrocarbyl, hydrocarbyloxfound: C 68.97 H 4.25 N 7.46 yhydrocarbyl, furyl, thienyl, and wherein R, can be either un- This compound was reduced into 3-phenylpiperidine b substituted or contain a halo substituent, which process comcatalytic reduction in acetic acid with Pto at 50 psi and at prises ga A-P m di n ic acid azide ofthe fonnula: room temperature. B.P. 80 C/l mm Hg.

. R2 R3 R4 Analysis (plcrate): &

calculated: C 52.30 H 4.62 N 14.35 R1 CH= s found: C 5257 H N 1440 wherein R1 R4 are as above, at an elevated temperature for a period of time sufficient to produce said 2-pyridone and EXAMPLE 8-1 1 thereafter recovering said 2-pyridone.

In a manner Similar to that employed in Example 7 2. The process of claign 1 wherein said temperature is from pyridines were prepared from the corresponding pyridone g Ti to about using POCl or POBr The starting materials, pyridines and I e pwcess o 6 1 wherem 531d -py ne IS 3- analytical data are set forth in Table 11 below: me y TABLE II Analysis Calculated Found Boiling Example Starting pyridorle Product point C H N C H N 8 3-phenyl2-pyridone 2-br0m0-3-phenylpyridine 104-105 56. 3.42 5. 99 55.80 3.57 5. 87 9 3-m-methoxyphenyl-2-pyrldone 2-chlor0-3-m-methoxyphenylpyridine 126-128 66.60 4.65 6.38 65.06 4.74 6. 39 10 3 (2-th1enyl)-2-p yrid0ne 2-011loro-3e(2-tllienyl)pyridine. (See Example 13) 11 3-(2 fury1)-2-pyrldone 2-chloro-3-(2-1uryl)-pyridlne (See Example 12) EXAMPLE 12 4. The process of claim 1 wherein said 2-pyridone is 3-pheny1-2-pyridone.

2-Chloro-3-(2-furyl)pyridine was transformed into 2- chlor'o-3(5-nitro-2- furyl)pyridine as follows:

Six g of 2-chloro-3-(2-furyl)pyridine were dissolved in 10 ml of acetic anhydride. To this solution maintained below 5 C., 6 ml of concentrated nitric acid were introduced. The mixture was then poured out on ice and the precipitate of nitro derivative was filtered and crystallized from light petroleum ether. M.p. 121 C. Yield: 66 percent.

5. The process of claim 1 wherein said 2-pyridone is 3-m- 40 methoxyphenyl-Z-pyridone.

6 The process of claim 1 wherein said 2-pyridone is 6-pmethoxyphenyl-3-phenyl-2-pyridone.

7. The process of claim 1 wherein said 2-pyridone is 3-( 2- thienyl)-2-pyridone.

8. The process of claim 1 wherein said 2-pyridone is 3-( 2-fu- Analysis: ryl)-2-pyridone.

calculated; c 4805 H 223 N 1245 g 9. A process for the preparation of 2-halogeno-pyridines of found: C47.96 H 2.43 N 12.39. the

R EXAMPLE 13 5Q 2-chloro-(2-thienyl)pyridine was transformed into 3-(2- R R4 thienyl)-pyridine as follows:

A mixture of 6 g of 2-chloro-3-(2-thienyl)pyridine, 6 g of R; N zinc and 150 ml of acetic acid was maintained to boiling for 3 I hours and then evaporated. The residue was taken up in X diluted NaOH and extracted with ethyl acetate. The organic layer was evaporated and the residue distilled at 95-100/l wheem RFRi each 18 carbon atoms and i dividually represent hydrogen, hydrocarbyl, hydrocarbylox- 85 Percent yhydrocarbyl, furyl, thienyl, and wherein R can be either uncalluh'ned C 67 00 H 4 35 N 8'70 substituted or contain a halo substituent, which process com- I 84 prises the steps of: I found C 67 01 H 4 48 N 5 1. heating a 2,4-pentadlenoic acid azide of the formula:

EXAMPLE 14 R3 R4 2-chloro-3(2-furyl)pyridine was transformed into 3-(2-fu- Rl H= Na ryl)pyn'dine in a manner similar to that employed in Example o 0 herein R -R are as above at an elevated temperature for 13. The product had a boiling point of 78 -79 C. at 0.1 mm w Hg and the following analysis (picrate): ahperlod olf tlme sufficient to produce the 2-pyr1done of calculated: 0 48.15 H 2.67 N 14.95 5 found: C 48.06 H 2.79 N 14.58 70 Although the invention has been illustrated by the preceedl ing examples, it is not to be construed as being limited to the materials employed therein but rather the invention encompasses the generic area as thereinbefore disclosed. Various 3, NH

modifications and embodiments thereof can be made without departing from the scope thereof. 0

wherein R,--R each contain up to 18 carbon atoms and individually represent hydrogen, hydrocarbyl, hydrocarbyloxyhydrocarbyl, furyl, thienyl, and wherein R can be either unsubstituted or contain a halo substituent, which process comprises the steps of:

1. heating a 2,4-pentadienoic acid azide of the formula:

wherein R,--R are as above, at an elevated temperature for a period of time sufficient to produce the Z-pyridone of the formula:

R1 NH 2.'contacting said Z-pyridone with POX wherein X is halogen and R,R., are, as above, to form the 2- halogenopyridine of the formula:

wherein X is halogen and R,--R. are as above, and 3. reducing said 2-halogenopyridine. 16. The process of claim 15 wherein said pyridine is '3-(2- thienyl)pyridine.

17. The process of claim 15 wherein said pyridine is 3-( 2-furyl )pyridine. 

2. The process of claim 1 wherein said temperature is from about 200* to about 300* C.
 2. contacting said 2-pyridone with POX3, wherein R1-R4 are as above, and X is halogen, and
 2. contacting said 2-pyridone with POX3, wherein X is halogen and R1-R4 are, as above, to form the 2-halogenopyridine of the formula:
 3. reducing said 2-halogenopyridine.
 3. recovering said 2-halogeno-pyridine.
 3. The process of claim 1 wherein said 2-pyridone is 3-methyl-2-pyridone.
 4. The process of claim 1 wherein said 2-pyridone is 3-phenyl-2-pyridone.
 5. The process of claim 1 wherein said 2-pyridone is 3-m-methoxyphenyl-2-pyridone.
 6. The process of claim 1 wherein said 2-pyridone is 6-p-methoxyphenyl-3-phenyl-2-pyridone.
 7. The process of claim 1 wherein said 2-pyridone is 3-(2-thienyl)-2-pyridone.
 8. The process of claim 1 wherein said 2-pyridone is 3-(2-furyl)-2-pyridone.
 9. A process for the preparation of 2-halogeno-pyridines of the formula:
 10. The process of claim 9 wherein said 2-halogeno-pyridine is 2-chloro-3-phenylpyridine.
 11. The process of claim 9 wherein said 2-halogeno-pyridine is 2-bromo-3-phenylpyridine.
 12. The process of claim 9 wherein said 2-halogeno-pyridine is 2-chloro-3-m-methoxyphenylpyridine
 13. The process of claim 9 wherein said 2-halogeno-pyridine is 2-chloro-3-(2-thienyl)pyridine.
 14. The process of claim 9 wherein said 2-halogeno-pyridine is 2-chloro-3-(2-furyl)pyridine.
 15. A process for the preparation of pyridines of the formula:
 16. The process of claim 15 wherein said pyridine is 3-(2-thienyl)pyridine.
 17. The process of claim 15 wherein said pyridine is 3-(2-furyl)pyridine. 